The present invention relates to improved methods of coating particulates with a resin composition so that they may be used in subterranean operations, such as hydraulic fracturing, gravel packing, and frac-packing.
Hydrocarbon-producing wells are often stimulated by hydraulic fracturing treatments. Hydraulic fracturing operations generally involve pumping a treatment fluid (e.g., a fracturing fluid or a “pad” fluid) into a well bore that penetrates a subterranean formation at a hydraulic pressure sufficient to create or enhance at least one or more fractures in the subterranean formation. The fluid used in the treatment may comprise particulates, which are often referred to as “proppant particulates,” that are deposited in the resultant fractures. The proppant particulates are thought to prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to a well bore to ultimately be produced. The term “propped fracture” as used herein refers to a fracture (naturally-occurring or otherwise) in a portion of a subterranean formation that contains at least a plurality of proppant particulates. The term “proppant pack” refers to a collection of proppant particulates within a fracture.
Hydrocarbon-producing wells also may undergo gravel packing treatments, inter alia, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particulates, often referred to in the art as gravel, are suspended in a treatment fluid, which may be viscosified, and the treatment fluid is pumped into a well bore in which the gravel pack is to be placed. As the particulates are placed in or near a subterranean zone, the treatment fluid is either returned to the surface or leaks off into the zone. The resultant gravel pack acts as a filter to prevent the production of the formation solids with the produced fluids. Traditional gravel pack operations may involve placing a gravel pack screen in the well bore and then packing the surrounding annulus between the screen and the well bore with gravel. The gravel pack screen is generally a filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations is available to suit the characteristics of a well bore, the production fluid, and any particulates in the subterranean formation.
In some situations, hydraulic fracturing and gravel packing operations may be combined into a single treatment. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Particulates (such as proppant or gravel) used in subterranean operations are often coated with resins to facilitate consolidation of the particulates and/or to prevent their subsequent flow-back through the conductive channels in the subterranean formation, which can, for example, clog the conductive channels and/or damage the interior of the formation or equipment. The term “resin” as used herein refers to any of numerous physically similar polymerized synthetics or chemically modified natural resins including thermoplastic materials and thermosetting materials.
A typical resin coating material is a two component resin system comprising a liquid hardenable resin component and a liquid hardening agent component. Heretofore, resin coated particulates have been coated by mixing both of the components of the resin system together on-the-fly to form a hardenable resin composition and then coating particulates with this hardenable resin composition at the well site. The term “on-the-fly” is used herein to mean that a flowing stream is continuously introduced into another flowing stream so that the streams are combined and mixed while continuing to flow as a single stream. Although this technique is frequently used to coat particulates, this method can be problematic. Once the two components of a resin coating material are mixed together to form a hardenable resin composition, the hardenable resin component becomes activated by the hardening agent component thus becoming tackified. As used herein, the term “tacky,” in all of its forms, generally refers to a substance having a nature such that it is (or may be activated to become) somewhat sticky to the touch. The hardenable resin composition may stick to equipment with which it may come into contact with during the particulate coating process or while being mixed into a treatment fluid thereby decreasing the efficiency of the coating process and making the equipment difficult to clean.
Another problem encountered in the use of hardenable resin compositions for coating particulates is that the hardenable resin composition has a very short shelf life. That is, once batch mixed, the shelf life of the hardenable resin composition may be as short as four hours or less. Heretofore, it has been a common practice to utilize particulates that have been precoated with a resin system where only a small portion of the resin remains curable, so that the resin pre-coated particulates can then be stored for later use. When the precoated particulates are required for use at a job site, they are then transported to the job site. However, when such precoated resin coated particulates are consolidated after being placed in a subterranean formation, the resulting consolidated particulates often do not have enough strength to prevent proppant flow-back and do not perform effectively.